Metal components suffer from a degree of residual stress caused by actions such as mechanical or thermal loading. The presence of stress affects the physical properties of a metal component and can result in stress fatigue and even failure of a component.
Methods available for measuring residual stress in metal components are not in widespread usage. Current practice is generally simply to subject a metal component to thermal stress relieving techniques regardless of the actual need. Therefore a significant wastage of resources arises in heat treating metal components not requiring stress relief.
A related problem arises with elongate components such as railway lines and pipelines. A railway track is generally laid in such a way as to be under a neutral load condition at a predetermined temperature. When the track is above the neutral temperature the railway line as a whole is placed under compression as the sections expand. At excessive levels this can result in the track buckling. At temperatures lower than the neutral temperature the track lengths exist in tension. At some point if the tensile forces are high enough, ie the temperature is low enough, the sections of track can snap.
Because of the outcome of the snapping of sections of track is not as much of a safety hazard as buckling of track the neutral temperature is typically set above the average summertime temperature. In New Zealand the neutral temperature is set at around 30 degrees Celsius.
Railway lines undergo considerable thermal cycling. They are also subjected to significant mechanical loading as trains ride over the rails. This can result in plastic deformation of the rails, that is, the rails stretch. When that happens the neutral temperature of the rails drops, and thus the risk of track buckling on hot days increases. It is generally accepted that railway lines need to be reset or restretched. More particularly, they need to be re-laid under tension in order to reset the neutral temperature every ten years or so to minimise the risk of buckling. At present it is a costly and time consuming exercise to uplift a railway line to restretch and relay it. Significant resources can be wasted on restretching sections of track that do not require any stretching.
It is an object of the invention to provide a device and/or an apparatus for use in testing the integrity of metal components and sections of railway line that overcomes at least some of the abovementioned problems, or at least to provide the public with a useful choice.